Canals, drainage ditches, irrigation channels, and the like frequently are contaminated with debris such as tree limbs, grass clippings, leaves, tires, beverage containers, plastic and textile bags, and various other kinds of trash. If such debris is permitted to enter a pump or other water treating apparatus, such apparatus could be seriously damaged. It is the practice, therefore, to protect such apparatus by mounting a stationary trash-collecting rack or screen in the stream of water upstream of the apparatus to be protected. Such a rack or screen, however, can become so clogged with trash and other debris as to prevent or severely restrict the flow of water through the rack to the pump or other apparatus.
To minimize the effects of rack clogging, it is customary to provide a mechanism for preventing the accumulation of debris on the screen. The known forms of anticlogging mechanisms employ a plurality of chains supported at their upper and lower ends by drums mounted on a rigid framework integral with the trash rack and supporting traveling debris-engaging fingers. Such a mechanism is disclosed in U.S. Pat. No. 4,709,804. Although this anticlogging mechanism functions well for its intended purpose, it does not remove debris which is of such nature as to slip by the chains and become plastered on the screen. That is, such mechanism does not perform a screen cleaning function.